1. Field Of The Invention
The present invention relates to the field of computer animation/graphics display systems. More particularly, the present invention relates to apparatus and methods for mixing animation sequences stored in compressed form in a standard digital storage system, and computer graphics generated by the computer employing a single line store to synchronize the decompressed animation sequences to the computer graphics.
2. The Prior Art
Many new multimedia applications require the presentation of animation sequences together with computer graphics on the same computer monitor. A dedicated animation sequence generator is used to decode the animation sequences stored in compressed form. Combining images delivered by the computer graphics generator and the animation sequence generator presents several problems.
The first problem relates to synchronization. The computer graphics generator outputs pixels at a certain pixel frequency (25 to 50 MHz), line frequency (35 kHz typically) and frame frequency (in excess of 70 Hz). In contrast, the animation sequence generator outputs pixels at typically a maximum frequency of 20 MHz, and a frame frequency of 25 or 30 Hz (a frame being typically 640.times.480 pixels). Before the computer graphics and the animation sequences can be combined, they have to be synchronized. Most of the time, the animation sequences have to be synchronized to the computer graphics. This is usually done by employing one or several frame stores, each frame store being implemented with dual port dynamic RAM (Video RAMs or VRAMs). This implementation results in a high product cost, since at least one megabyte of expensive VRAMs have to be used.
It is desirable for the animation images to occupy only part of the computer screen. Therefore, the animation images have to be resized dynamically in real time. This resizing usually requires one frame store, with its addition to the cost of the product. Moreover, resampling must be followed by filtering if a good quality animation image is to be displayed. Temporal filtering in particular requires simultaneous access to corresponding lines from consecutive frames. This usually requires n frame stores, if an n-order temporal filter is to be implemented. This results in a geometric increase of the memory requirement, and the cost of the product, as more sophisticated temporal filtering is implemented.
In some applications, it is desirable to simultaneously present on the computer screen several animation sequences mixed with the computer graphics. This usually requires the use of several animation sequence generators, thereby increasing considerably the cost of the product and the complexity of the hardware design.